Peak voltage indicator and regulator



Efi, 19%, H Q LEKEL V 2,4G3fi8g PEAK VOLTAGE INDICATOR AND REGULATOR Original Filed Oct. 16, 194 3 5 Sheets-Sheet l Fgoi Mam I l 7 HAWEaY cmzmas mm INVENTOR.

A05 A TTO zmwa July M, 39%. H. c. LIKEL PEAK VOLTAGE INDICATOR AND REGULATOR 5 Sheets-$heet 2 Original Filed Oct. 16, 1945 HARRY crmmzm LEAEL.

INS'ENTOR.

BY v Q M 7 #15 A-r-wnm eys Jmfiy 11, 1945. H c LIKEL Zfifiig PEAK VOLTAGE INDICATOR AND REGULATOR Original Filed Oct. 16, 1943 3 Sheets-Sheet 3 Imam! CHARLES Lucas.

Patented July 16, 1946 PEAK VOLTAGE INDICATOR AND REGULATOR Harry Charles Like], Brooklyn, N. Y.

Original application October 16, 1943, Serial No. 506,500. Divided and this application July 11, 1944, Serial No. 544,447

7 Claims.

The present invention relates to an indicator for showing which of several peak voltages is the highest, second highest, third highest, etc., and also comprehends the application of the indicator as a means for regulating the artificial line resistance of a duplex telegraph circuit both man.- ually and automatically.

This application is a division of my copending application Serial No. 506,500, filed October 16, 1943.

In the following description the indicator is shown as applied to a duplex telegraph circuit although it may be utilized to indicate the relationship between peak voltages in other circuits. For example, the indicator may be utilized for indicating the peak voltage relationships between the phases of a polyphase system or for determining the value and order in which peak voltages occur between the cathodes and the anodes of a multiphase rectifier.

As regards the indication of peak voltages in the line and artificial line legs of a duplex telegraph system, the application is to the method, disclosed in copending application of Alder F. Connery, Serial No. 494,172, filed July 10, 1943, for Duplex balance indicator. In general this method depends upon the voltage relationships occurring between an arbitrarily selected point on a resistance in the real line leg of a duplex circuit and two points on a resistance in the artificial line leg, the latter two points being so selected that the maximum voltages occurring between each one of these points and the point in the real line will, when the system is in balance, be equal.

It is an object of my invention to provide a peak voltage indicator which will show the relationship between voltages occurring in two or more related branches of a circuit.

It is another object of my invention to provide a peak voltage indicator which will show the relationship between peak voltages occurring in separate circuits.

It is a further object of my invention to provide an automatic regulator operated by a peak voltage detector, this regulator being adapted to alter the constants in one of two circuits to make the peak voltages occurring in the two circuits equal.

It is a still further object of my invention to provide such a regulator as that mentioned above particularly adapted to automatically regulate the artificial line resistance of a duplex telegraph circuit.

Further objects and features will appear when the following description is considered in connection with the annexed drawings, in which Figure 1 is a schematic diagram of a peak of my invention voltage indicator applied for line balancing ac- 450 cording to the method of copendingapplication of Alder F. Connery, Serial No. 494,172, showing the connections thereof to one terminal of a duplex telegraph circuit;

Figure 2 is a schematic diagram of one form of automatic regulator for adjusting the artificial line resistance of a duplex telegraph circuit in accordance with the peak voltages occurring in the circuit; and

Figure 3 is a schematic diagram of an alternative circuit for balancing the two vacuum tubes for the two circuits of the duo-triode of Figures 1 and 2.

Referring now to Figure 1, there is shown in the upper part of that figure the telegraph equipment for one terminal of a duplex telegraph circuit. In these drawings I 0 and II represent the windings of the diirerential relay of a differential type duplex or the bridge arms of 'a bridge type duplex set. Asis customary, one of these windings or bridge arms, as the case may be, as I0, is connected to the real line and the other, I I, to the artificial line. Also as is usual, the opposite terminals of the two relay windings or bridge arms are connected together and to the transmitting key I2 (this may, of course, be the tongue of a transmitting relay). The key I2 is connected by means of conductors I3 and I4 to limiting resistance I5 and I6 and thence to the batteries I1 and I8 which are oppositely poled as is cutomary. Batteries I7 and I8 are connected to ground or to a metallic return 20, this also being in accordance with usual practice.- In this instance, resistances 2I and Here put in series with the windings or arms I0" and II respectively in order to lessen the effects of the mutual inductance between'the windings I0 and II on the peak voltage indicator, and to increase the resistance of the legs of the circuit across which the indicator i connected.

The Voltage divider 23 is center tapped at. 24 and connected by means of a conductor 25' to the split of the duplex at 26. The ends of the divider are connected by means of conductors 27 and 28 to the two legs of the duplex. Divider 23'is also tapped at points 30 and 3|, point 3I being electrically twice as far removed from the left end of the divider, as shown in Figure 1, as is point 30 from the right end. As is explained in detail in the Connery application above mentioned, when the artificial line is in proper balance, the peak voltages occurring between points 30 and 3| and points 30 and 32 will be equal.

The indicator of the present invention is shown in the lower part of Figure l, and comprises the two vacuum tubes 33 and 34 together with the glow tubes 35 and 36 and their associated cir cuits. The control grid of Vacuum tube 33 is connected by means of potentiometer circuit 31 (comprising the potentiometer 38 and batteries 40 nected by means of conductors 46 and 41 to the i plate supply battery 43.

The grid-cathode circuit of tube 33 is supplied with its operating potential by battery 56, potentiometer 5|, the voltage between points 36 and 3 I and potentiometer circuits 31.

In a similar manner, the grid of vacuum tube 34 is connected by means of conductor 54 to point 32 of the potentiometer and the plate of this tube is connected by means of conductor 55 to the load circuit comprising glow lamp 36, resistance 56 and condenser 51. The load circuit is in turn connected by means of conductors 58 and 41 to the plate battery 48. The cathode of tube 34 is connected by means of conductor 52 to the battery 56 and potentiometer 5| being exactly similar in this respect to the corresponding circuit of tube 33. i

The voltage in the grid-cathode circuit of vacuum tube 34 in the bias voltage supplied by potentiometer 5| (in accordance with the adjustment of contact 6| thereon) plus the voltage occurring between points 30 and 32.

Hereinafter the voltage supplied by potentiometer 5i will be designated as E and that supplied by potentiometer 31 as Eb.

If now the potentiometer is adjusted so that the total voltages in the grid circuits of tubes 33 and 34 are beyond the cut off point When the voltage divider 23 is not connected to the telegraph circuit, then upon connecting the divider to the telegraph circuit if a voltage is developed by the incoming signal across voltage divider 23 with its positive polarity toward point 32 and the transmitting relay tongue or the transmitting key I2 is on the positive contact, the voltage appearing between points 30 and 3! will be at its maximum value with positive toward the grid of vacuum tube 33.

If the incoming signal remains the ame but the transmitting key i2 is moved into contact with the negative battery the voltage appearing between points 30 and 32 of voltage divider 23 will be at its maximum value with positive toward the grid of tube 34. If now the voltage EC is slowly reduced in magnitude making the grids of the two tubes 33 and 34 less negative, either the grid of tube 33 or that of tube 34 or both will be driven into the conducting region in turn as the voltage conditions discussed above and in greater detail in the Connery application above mentioned come about through the operation of the telegraph circuit. As either tube conducts the voltage across its load circuit comprising glow lamp 35, resistance 45 and condenser 44 in one case and glow lamp 36, resistance 56 and condenser 51in the other, will rise until the particular glow lamp flashes. Since the voltage Eb is so adjusted that with no voltage existing across the main and artificial lines both glow' lamps would light at the same setting of the potentiometer 5|, it will be clear that as E0 is slowly reduced, lamp 35 will flash before lamp 36 if the resistance of the artificial line is too high. Conversely lamp 36 of the artificialline is too low; Moreover if the resistance of the artificial line is correct for balance, lamps 35 and 36 will flash in an irregular alternate manner depending upon the combinations of the received and. transmitted signals.

will flash first if the resistance- The load condensers 44 and 51 serve two purposes. They prevent a too rapid build up of voltage across the respective load resistances 45 and 56 and the lamp 3'5 and 36 in response to spurious voltages of short duration in the grid circuits of tubes 33 and 34 and, furthermore, they provide reservoirs of current to assure a bright flash of the associated glow lamps when they ionize.

Asshown in Figure 1, there are two additional condensers 64 and 65 which are connected across points 3i and 32' and 30 and 32 of the voltage divider 23 respectively. These two condensers are for the purpose of reducing the voltages developed between points 3| and S5 and 33 and 32 during transient conditions such as those caused by static unbalance or noise conditions.

As was indicated above the procedure in using my device is as follows. First the measuring circuits for the low and high sides must be balanced. To effect this the tubes 33 and 34 are switched on and with no connections to the telegraph circuit the bias voltage E0 is made less negative by adjustment of contact 6| on potentiometer 51 until either lamp 35 or 36 ignites. If lamp 35 ignites the voltage ,Eb is made more negative whileif lamp 36 ignites this voltage is made more positive. Contact 6| i then again adjusted until the voltage supplied by potentiometer 5i is sufficiently negative to cause the extinguishment of the lighted lamp. This procedure is repeated until upon reducing EC both lamps simultaneously ignite. are balanced and ready for use.

The connections of the leads 25, 27 and 28 to the telegraph circuit, as shown in Figure 1, are next made. The unit is now ready for use in balancing the telegraph circuit. Contact 6! is at this time adjusted to make the biasing Voltage E0 a maximum and prevent either of the lamps 35 or 36 from lighting. Next E3 is slowly reduced by adjustment of contact 6! until one or both of the lamps begin to flash. If the artificial line resistance is set at too low a value lamp 33 will flash, this lamp, of course, being suitably marked to indicate that its ignition represents a condition of the circuit in which the artificial line resistance is too low. Thereupon the artificcial line resistance is increased in value by some suitable amount, say 50 ohms. If this causes the lamp 36 to stop flashing and the lamp 35 to begin to flash, it indicates that the proper value oi artificial line resistance is somewhere between the old and new values. The resistance is so set and checked by repeating the adjustment of the contact 6| to show that both lamps now flash.

In some instances, it is preferable to adjust the artificial line resistance automatically rather than to merely indicate that such adjustment should be made. In Figure 2, there is shown an arrangement for accomplishing such automatic adjustment. In this figure the voltage divider 23 is identical with that of Figure 1 and is connected to the telegraph circuit in exactly the same I manner. Furthermore, in this figure the two pentode tubes 33 and 34 of Figure l have been replaced 'with a duo-triode 66, having two plates 61 and 68 and two grids l0 and II. It will, therefore be clear that in effect this duo-triode 66 is the equivalent of the two tubes 33 and 34. The grids l0 and H of the tube are connected to points 3| and 32 of the voltage divider 23 by means of leads 42 and 54 in a manner exactly similar to .the connection of the grid fof the pentodes of When this occurs the circuits,

Figure 1 to the voltage divider 23. In place of the output or load circuits comprising the lamps and 35, resistances and and condensers 44 and 5?, there are supplied two breakover relays I2 and I3, the windings of which are respectively connected to the plates 68 and 61 of the duo-triode 65. Upon operation of either of these relays and considering relay 12 as an example, it will be seen that a short circuit is removed from the associated magnet I4 of an artificial line resistance adjusting device generally designated I5.

The resistance adjusting device 15 comprises a rheostat I6 having a rotatable contact 11 mounted upon a shaft I8 upon which are also mounted for rotation therewith the two ratchet wheels 80 and 8|. Cooperating with the ratchet wheel 80 is a resilient pawl 82 made integral with the armature 83 of the magnet 14. In like manner, a resilient pawl 81; integral with armature 05 of magnet 86 cooperates with the ratchet wheel 3 I. The rheostat IE is substituted for the normal adjustable artificial line resistance and is connected through a movable contact 11 to ground or to the return lin by means of conductor 81., the rheostat 75 being connected at its other terminus to the artificial line end of the duplex differential relay or duplex bridge arm such as I I of Figure 1.

It will be clear that when magnet 14 is operated, the artificial line resistance is increased and when magnet 86 is operated the resistance is decreased. As was indicated above, magnet 14 is operated upon the operation of break over relay 12. However, the circuit for operating this magnet was not traced in detail above but will be in the following. Normally both magnets I4 and 80 are short circuited by virtue of the normally closed position of the contacts of relays 12 and 73. When relay I2 is in its normal position a circuit is completed from the battery 90 over conductor 9|, resistance 02, conductor 93 to the contact and tongue of rela 12 to conductor 94 and thence over conductors 95, 96, 91 and 98 to the opposite side of the battery. In a like manner, when relay I3 is in its normal position a circuit is completed from battery 90, conductor I00, resistance IOI, conductor I02, contact and tongue of relay is to conductor 94 and thence over the path just above traced in connection with relay 72 to the opposite Side of battery 00. Upon operation of relay 12 the circuit above traced for it is broken at its tongue and contact and the short circuit removed from magnet 14, the. operating circuit for this magnet then extending from resistance 92 through conductor I03 to the magnet and thence over conductor 98 to the opposite side of the battery 90. In the identical manner the operation of relay I3 removes the short circuitfrom the magnet 86 and permits its energization over a circuit extending from resistance IOI through conductor I04 and the magnet winding to conductor 98 and the opposite side of battery 90. It will be obvious from the description of Figure 1 that when the artificial line resistance is too high it causes energization of breakover relay 13 which in turn causes operation of magnet 85 and clockwise rotation of shaft 70, thereby lowering the artificial line resistance. Conversely when the artificial line re-.

sistance is too low breakover relay I2 is energized to in turn energize magnet 14 and increase the artificial line resistance.

Due to the fact that a change in the line balance is usually if not invariably accompanied 075 by a change in the voltage level o the line, the voltage Ec which was previously (in the circuit of Figure 1) manually adjusted, must now be authomatically adjusted if the circuit is to operate without supervision. For this purpose, two relays I05 and I06 are provided, these relays being respectively operated by the operation of break over relays I2 and I3. Relays I05 and I06 are adapted to place bias upon the grids 10 and II of the duotriode 65. Considering now relay I05 it will be seen that this relay is operated at the time when the short circuit is removed from magnet M as above described, the winding of relay I05 being in parallel with the winding of magnet M. Likewise relay IE6 is operated when break over relay 13 operates, its winding being in parallel with the winding of magnet 86 and the short circuit being removed from its winding at the time of operation of relay 23. Upon operation of relay I05 a circuit is completed from biasing battery I I0 through conductors III and H2, closed contact and tongue of relay I05, conductor II3, resistance I07 and condenser I08 in parallel, and resistance H4 to the other pole of battery H0. Essentially the same circuit is completed upon the operation of relay I05. The closure of the circuit just above traced raises the bias voltage E0 which decreases as the charge on condenser I08 is dissipated. Thus, as the line level changes, the bias voltage Ec is caused to be raised and lowered through a range in the same manner as manual adjustment was made in connection with the circuit of Figure 1. Under suitable line conditions, first one break over relay will operate and then the other, causing the artificial line resistance to hunt by the amount represented by one tooth of the ratchet wheels and 8|.

In some instances it is preferable to equalize the output of the two tubes 33 and 34 or to equalize the output of the two plate circuits 6! and 68 of the duo-triode 66 by adjusting their plate potentials rather than by the adjustment of the grid voltage. In this case the potentiometer 37 of Figures 1 and 2 is omitted and a potentiometer I20, Figure 3, is provided in the plate circuits of the two tubes. It will be seen that by adjusting the contact I2I on the potentiometer I20 and the voltage applied to the plates 6'! and 60 of the duo-triode 66, the output of these tubes may be made equal so that the indicators in the load circuit, whether these indicators be the glow lamps 35 and 35 as shown in Figure 3 or the break over relays I2 and 13 of Figure 2, will ignite under the same peak voltage conditions in the circuits under test. When such a potentiometer I20 is used it is preferable to utilize resistances I22 and I23 across the battery 40 in order that current may be flowing at all times in the potentiometer and in order that the potentiometer resistance may be less than would otherwise be necessary. These two bleeding resistances I22 and I23 should be of equal value.

As was indicated above, and as will be obvious to those skilled in the art, the potentiometer I20 may be utilized as an equalizing circuit in connection with the automatic regulator of Figure 2, as well as in connection with the indicator of Figure 1. As will also be obvious, either the duotriode of Figures 2 and 3, or the two tube arrangement of Figure 1 is susceptible to this mode of adjusting the output to cause operation of the glow lamps or break over relays under the same voltage conditions of the two circuits under test. It will be understood, however, that if the two tube arrangement is used the tubes must be triode tubes since with pentode tubes the plate voltage change will not be effective.

While I have described preferable embodiments of my invention it will be understood that many additional modifications are possible. Moreover, it will be clear that instead of indicating the eak voltages in circuits having a common leg, it is entirely possible by mechanically interconnecting potentiometers such as of Figures 1 and 3, to indicate the relative value of peak voltages occurring in entirely separate circuits. Again the comparison need not be between two circuits only, but may be extended by the addition of vacuum tubes and indicators to as many circuits as may be desirable. It will, of course, be understood that in this instance all tub-es except one would be supplied with a potentiometer circuit such as 31 of Figure l, or the equivalent thereof shown in Figure 3, in order that the vacuum tubes might be adjusted to operate under the identical peak load conditions. Consequently the scope of my invention is to be determined not by the foregoing description, but solely by the annexed claims.

What is claimed is:

1. In a device for regulating the artificial line resistance of a duplex telegraph circuit, in combination, a voltage divider having a center tap and adapted to have said center tap connected to the split of the duplex and its ends connected one to the real line and one to the artificial line of the duplex, said voltage divider having two additional taps the first one of which is located a predetermined electrical distance from the main line connection of the divider and the second one of which is located twice that electrical distance from the artificial line end of the voltage divider, a pair of electron tubes each having an input circuit and an output circuit, the input circuit of one of said tubes including that portion of the voltage divider between said first and said second mentioned additional taps, the input circuit of the second electron tube including that portion of the voltage divider between the first mentioned additional tap and the artificial line end of the voltage divider, means in the output circuit of each of said electron tubes, said means being operable only upon the application thereto of a certain minimum voltage, means to adjust the output of one of said tubes to cause both said output means to function upon the application of a particular voltage to the corresponding electron tube input circuit, means to connect said voltage divider to said duplex circuit, and means operated by said output means individually one to vary the artificial line resistance in one direction and the other in the opposite direction to thereby maintain the artificial line in balance with the real line.

2. In a device for regulating the artificial line resistance of a duplex telegraph circuit, in combination, a voltage divider having a center tap and adapted to have said center tap connected to the split of the duplex and its ends connected one to the real line and one to the artificial line of the duplex, said voltage divider having two additional taps the first one of which is located a predetermined electrical distance from the main line connection of the divider and the second one of which is located twice that electrical distance from the artificial line end of the voltage divider, a pair of electron tubes each having an input circuit and an output circuit, the input circuit of one of said tubes including that portion of the voltage divider between said first and said second mentioned taps, the input circuit of the second electron tube including that portion of the voltage divider between the first mentioned tap and the artificial line end of the voltage divider, relay means in the output circuit of each of said electron tubes, said relay means being operable only upon the application thereto of a certain minimum voltage, means to adjust the output of one of said tubes to cause both said relay means to function upon the application of a particular voltage to the corresponding electron tube input circuit, means to connect said voltage divider to said duplex circuit, and means operated by each of said output relay means to vary the artificial line resistance in opposite directions to thereby maintain the artificial line in balance with the real line.

3. In a device for regulating the artificial line resistance of a duplex telegraph circuit, in combination, a voltage divider having a center tap and adapted to have said center tap connected to the split of the duplex and its ends connected one to the real line and one to the artificial line of the duplex, said voltage divider having two additional taps the first one of which is located a predetermined electrical distance .from the main line connection of the divider and the second one of which is located twice that electrical distance from the artificial line end of the voltage divider, a pair of electron tubes each having an input circuit and an output circuit, the input circuit of one of said tubes including that portion of the voltage divider between said first and said second mentioned taps, the input circuit of the second electron tube including that portion of the voltage divider between the first mentioned tap and the artificial line end of the voltage divider, breakover relays in the output circuit of each of said electron tubes, said breakover relays being operable only upon the application thereto of a certain minimum voltage, means to adjust the output of one of said tubes to cause both said breakover relays to function upon the application of a particular voltage to the corresponding electron tube input circuit, means to connect said voltage divider to said duplex circuit, and means operated by said output breakover relays to vary the artificial line resistance in opposite directions to thereby maintain the artificial line in balance with the real line,

4. In a device for regulating the artificial line resistance of a duplex telegraph circuit, in combination, a voltage divider having a center tap and adapted to have said center tap connected to the split of the duplex and its ends connected one to the real line and one to the artificial line of the duplex, said voltage divider having two additional taps the first one of which is located a predetermined electrical distance from the main line connection of the divider and the second one of which is located twice that electrical distance from the artificial line end of the voltage divider. a pair of electron tubes each having an input circuit and an output circuit, the input circuit of one of said tubes including that portion of the voltage divider between said first and said second mentioned taps, the input circuit of the second electron tube including that portion of the voltage divider between the first mentioned tap and the artificial line end of the voltage divider, means in the output circuit of each of said electron tubes, said means being operable only upon the application thereto of a certain minimum voltage,

'means to adjust the output of one of said tubes to cause both said output means to function upon the application of a particular voltage to the corresponding electron tube input circuit, means to connect said voltage divider to said duplex circuit, an adjustable artificial line resistance, means under the control of one of said output means for adjusting said resistance to lessen the magnitude thereof, means operable by the other of said output means for adjusting said resistance to increase the magnitude thereof, and means operable upon the operation of either of said output means for decreasing and thereafter gradually increasing the output of both of said tubes to compensate for the changed line and artificial line voltages resulting from the adjustment of said artificial line resistance.

5. In a device for regulating the artificial line resistance of a duplex telegraph circuit, in combination, a voltage divider having a center tap and adapted to have said center tap connected to the split of the duplex and its ends connected one to the real line and one to the artificial line of the duplex, said voltage divider having two additional taps the first one of which is located a predetermined electrical distance from the main line connection of the divider and the second one of which is located twice that electrical distance from the artificial line end of the voltage divider, a pair of electron tubes each having an input circuit and an output circuit, the input circuit of one of said tubes including that portion of the voltage divider between said first and said second mentioned taps, the input circuit of the second electron tube including that portion of the voltage divider between the first mentioned tap and the artificial line end of the voltage divider, means in the output circuit of each of said electron tubes, said means being operable only upon the application thereto of a certain minimum voltage, means to adjust the output of one of said tubes to cause both said means to function upon the application of a particular voltage to the corresponding electron tube input circuit, means to connect said voltage divider to said duplex circuit, an adjustable artificial line resistance, means under the control of one of said output means for adjusting said resistance to lessen the magnitude thereof, means operable by the other of said output means for adjusting said resistance to increase the magnitude thereof, means comprising a pair of relays operated respectively by said output means and a source of potential and condenser inserted in the input circuits of said electron tubes for decreasing and thereafter gradually increasing the output of both of said tubes to compensate for the changed line and artificial line voltages resulting from the adjustment of said artificial line resistance.

6. In a device for regulating the artificial line resistance of a duplex telegraph circuit, in combination, a voltage divider having a center tap and adapted to have said center tap connected to the split of the duplex and its ends connected one to the real line and one to the artificial line of the duplex, said voltage divider having two additional taps the first one of which is located a predetermined electrical distance from the main line connection of the divider and the second one of which is located twice that electrical distance from the artificial line end of the voltage divider, a pair of electron tubes each having an input circuit and an output circuit, the input circuit of one of said tubes including that portion of the voltage divider between said first and said second mentioned taps, the input circuit of the second electron tube including that portion of the voltage divider between the first mentioned tap and the artificial line end of the voltage divider, means in the output circuit of each of said electron tubes, said means being operable only upon the application thereto of a certain minimum voltage, means comprising a potentiometer in the input circuit of one of said tubes to adjust the output of said tube to cause both said means to function upon the application of a particular voltage to the corresponding electron tube input circuit, means to connect said voltage divider to said duplex circuit, an adujstable artificial line resistance, means under the control of one of said outut means for adjusting said resistance to lessen the magnitude thereof, means operable by the other of said output means for adjusting said resistance to increase the magnitude thereof, means comprising a pair of relays operated respectively by said output means and a source of potential and condenser inserted in the input circuits of said electron tubes for decreasing and thereafter gradually increasing the output of both of said tubes to compensate for the changed line and artificial line voltages resulting from the adjustment of said artificial line resistance.

7. In a device for regulating the artificial line resistance of a duplex telegraph circuit, in combination, a voltage divider having a center tap and adapted to have said center tap connected to the split of the duplex and its ends connected one to the real line and one to the artificial line of the duplex, said voltage divider having two additional taps the first one of which is located a predetermined electrical distance from the main line connection of the divider and the second one of which is located twice that electrical distance from the artificial line end of the voltage divider, a pair of electron tubes each having an input circuit and an output circuit, the input circuit of one of said tubes including that portion of the voltage divider between said first and said second mentioned taps, the input circuit of the second electron tube including that portion of the Voltage divider between the first mentioned tap and the artificial line end of the voltage divider, means in the output circuit of each of said electron tubes, said means being operable only upon the application thereto of a certain minimum voltage, means comprising a potentiometer in the output circuit of one of said tubes to adjust the output of said tube to cause both said means to function upon the application of a particular voltage to the corresponding electron tube input circuit, means to connect said voltage divider to said duplex circuit, an adjustable artificial line resistance, means under the control of one of said output means for adjusting said resistance to lessen the magnitude thereof, means operable by the other of said output means for adjusting said resistance to increase the magnitude thereof, means comprising a pair of relays operated respectively by said output means and a source of potential and condenser inserted in the input circuits of said electron tubes for decreasing and thereafter gradually increasing the output or both of said tubes to compensate for the changed line and artificial line voltage resulting from the adjustment of said artificial line resistance.

HARRY CHARLES LIKEL. 

